A Schottky diode is a unipolar device using electrons as carriers, which is characterized by high switching speed and low forward voltage drop. However, the Schottky diodes have limitation of relatively high reverse leakage current. The characteristics of the Schottky barrier are determined by the metal work function of the metal electrode, the band gap of the intrinsic semiconductor, the type and concentration of dopants in the semiconductor layer, and other factors. In contrast to the Schottky diode, a PN junction diode is a bipolar device that can pass more current than the Schottky diode. However, the PN junction diode has a forward voltage drop higher than that of the Schottky diode, and takes longer reverse recovery time due to a slow and random recombination of electrons and holes during the recovery period.
A Schottky rectifier device has been described in U.S. Pat. No. 6,710,418 to overcome the current leakage problem. Please refer to FIG. 1, a schematic diagram illustrating the Schottky rectifier device with insulation-filled trenches. The Schottky rectifier device 100 includes a heavily-doped N-type substrate 102, a lightly-doped N-type epitaxial layer 104 overlying the substrate 102, and a plurality of insulation-filled trenches 114 extending from the top surface of the epitaxial layer 104. There are two P-type silicon strips 108 on sidewalls of each trench 114. An anode electrode 110 is provided on the top surface of the epitaxial layer 104 and a cathode electrode 116 is provided on the bottom surface of the substrate 102. The anode electrode 110 forms a Schottky contact with the underlying epitaxial layer 104, and is in contact with the P-type silicon strips 108.
In the Schottky rectifier device 100, the Schottky contact between the anode electrode 110 and the epitaxial layer 104 results in low forward voltage drop. Furthermore, the P-type strips 108 can prevent the low accumulation threshold to reduce the current leakage problem of the Schottky rectifier device 100. However, the P-type strips 108 occupy some areas of the Schottky contact, and thus the size of the Schottky rectifier device 100 should be enlarged to keep the equivalent area of the Schottky contact to prevent increasing the forward voltage drop and consuming more power. Therefore, an improved Schottky rectifier device with low current leakage but without increasing the size thereof is desired. There is a need of providing the improved Schottky rectifier device in order to obviate the drawbacks encountered from the prior art.